Once you download the app, you need to sign up this is free. Once you signed up you will see offers, there is the cheerios one there this can only be used once though. To receive your 50p reward, you need to answer a simple question, then scan the barcode to make sure it's correct product and when you get home upload the receipt. Once done you will see 50p in your shopitize account. You can get a payout when you reach £5+ this can be via PayPal or bank transfer :)

Shopitize gives you exclusive offers when you sign up to, I've read that you could get 4 Pints of milk for free + kettle crisps etc.